A section of the HS2 high-speed rail link in west London will run in a tunnel, the government has said.
The 5.6 mile (9km) tunnel section will run under Ealing and Northolt, between the interchange station at Old Oak Common and Northolt.
HS2 said the tunnel would cut the building timetable by 15 months and reduce disruption to residents and traffic at Hanger Lane.
The decision was the "best solution for this part of the route", it added.
The new tunnel will link a previously planned tunnel to and from West Ruislip in west London.
Transport minister Robert Goodwill said that some land could be affected by the construction and landowners may be able to apply for compensation.
An HS2 spokesman said: "By running our trains through a tunnel here we will save time during construction and there will be less disruption to residents, businesses and on local roads, particularly at Hanger Lane."
The government also announced that a tunnel would be constructed under the M6 viaduct at Bromford to take the high-speed line into Birmingham.